Improve the fix attempt

Author: fredericDelaporte

src/NHibernate/Hql/Ast/ANTLR/Tree/DotNode.cs

@@ -405,8 +405,7 @@ private void DereferenceEntity(EntityType entityType, bool implicitJoin, string
 			// For nullable entity comparisons we always need to add join (like not constrained one-to-one or not-found ignore associations).
 			// For property-ref associations, we also need this unless finding a way in the IdentNode for the other hand of the comparison
 			// to detect it should yield the property-ref columns instead of the primary key columns.
-			bool comparisonWithNullableEntityOrThroughPropertyRef = Walker.IsComparativeExpressionClause
-				&& (entityType.IsNullable || entityType.IsUniqueKeyReference);
+			var comparisonWithNullableEntity = Walker.IsComparativeExpressionClause && entityType.IsNullable;
 
 			if ( IsDotNode( parent ) ) 
 			{
@@ -415,7 +414,7 @@ private void DereferenceEntity(EntityType entityType, bool implicitJoin, string
 				// entity's PK (because 'our' table would know the FK).
 				parentAsDotNode = ( DotNode ) parent;
 				property = parentAsDotNode._propertyName;
-				joinIsNeeded = generateJoin && ((Walker.IsSelectStatement && comparisonWithNullableEntityOrThroughPropertyRef) || !IsReferenceToPrimaryKey( parentAsDotNode._propertyName, entityType ));
+				joinIsNeeded = generateJoin && ((Walker.IsSelectStatement && comparisonWithNullableEntity) || !IsReferenceToPrimaryKey( parentAsDotNode._propertyName, entityType ));
 			}
 			else if ( ! Walker.IsSelectStatement ) 
 			{
@@ -429,14 +428,15 @@ private void DereferenceEntity(EntityType entityType, bool implicitJoin, string
 			else
 			{
 				joinIsNeeded = generateJoin || (Walker.IsInSelect && !Walker.IsInCase) || (Walker.IsInFrom && !Walker.IsComparativeExpressionClause)
-				               || comparisonWithNullableEntityOrThroughPropertyRef;
+				    || comparisonWithNullableEntity || !entityType.IsReferenceToPrimaryKey;
 			}
 
 			if ( joinIsNeeded )
 			{
-				var forceLeftJoin = comparisonWithNullableEntityOrThroughPropertyRef && !IsCorrelatedSubselect;
+				// Subselect queries use theta style joins, which cannot be forced to left outer joins.
+				var forceLeftJoin = comparisonWithNullableEntity && !IsCorrelatedSubselect;
 				DereferenceEntityJoin(classAlias, entityType, implicitJoin, parent, forceLeftJoin);
-				if (comparisonWithNullableEntityOrThroughPropertyRef)
+				if (comparisonWithNullableEntity)
 				{
 					_columns = FromElement.GetIdentityColumns();
 				}